将图像添加到空布局 jpanel

Question

我希望将吃豆人的JPEG图像添加到空布局JPanel中，以便我可以使用密钥侦听器来移动图像。这是我到目前为止的代码：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.imageio.*;
import java.awt.image.*;
import java.io.*;
public class PacmanCharacterMovement2{
  static BufferedImage pacman;
  static int xCoor;
  static int yCoor;
  public static class PacmanPanel extends JPanel implements KeyListener {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(pacman, xCoor, yCoor, null);
    }
    public void keyTyped(KeyEvent e) {
    }
    public void keyPressed(KeyEvent e) {
      if (e.getKeyCode() == KeyEvent.VK_UP) {
        xCoor = xCoor--;
        yCoor = yCoor;
      }
      else if (e.getKeyCode() == KeyEvent.VK_DOWN) {
        xCoor = xCoor++;
        yCoor = yCoor;        
      }
      else if (e.getKeyCode() == KeyEvent.VK_LEFT) {
        xCoor = xCoor;
        yCoor = yCoor--;      
      }
      else if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
        xCoor = xCoor;
        yCoor = yCoor++;        
      }
      else{}
      repaint();
    }
    public void keyReleased(KeyEvent e) {
    }
  }
  public static void main(String[] agrs){
    try {
      pacman = ImageIO.read(new File("PacmanCharacter2.jpg"));
    } catch (IOException e) {}
    xCoor = 30;
    yCoor = 30;
    JFrame window = new JFrame ("Pacman Movement");
    JPanel pacmanPanel = new JPanel ();
    pacmanPanel.setLayout(null);
    PacmanPanel mainPanel = new PacmanPanel();
    window.setContentPane(mainPanel);
    window.setSize(600,450);
    window.setLocation(350,150);
    window.setVisible(true); 
  }                                                           
}

图像出现在屏幕上，但不移动。

Answer 1

您需要使用键盲而不是AWT KeyEvents，因为AWT KeyEvent需要焦点才能收听事件，而且xCoor = xCoor--;不像您期望的那样工作，您应该使用xCoor--;或xCoor = xCoor-1;。这是您可以为所有箭头键编写up键的示例......

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.imageio.*;
import java.awt.image.*;
import java.io.*;
public class PacmanCharacterMovement2 {
    static BufferedImage pacman;
    static int xCoor=30;
    static int yCoor;
    public static class PacmanPanel extends JPanel {
        public PacmanPanel() {
            this.getInputMap().put(KeyStroke.getKeyStroke("UP"), "doup");
            this.getActionMap().put("doup", new AbstractAction("doup") {
                public void actionPerformed(ActionEvent evt) {
                    xCoor--;
                    yCoor = yCoor;
                    repaint();
                }
            }
            );
        }
        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawImage(pacman, xCoor, yCoor, null);
        }

    }
    public static void main(String[] agrs) {
        try {
            pacman = ImageIO.read(new File("PacmanCharacter2.jpg"));
        } catch (IOException e) {
        }
        xCoor = 30;
        yCoor = 30;
        JFrame window = new JFrame("Pacman Movement");
        PacmanPanel mainPanel = new PacmanPanel();
        window.setContentPane(mainPanel);
        window.setSize(600, 450);
        window.setLocation(350, 150);
        window.setVisible(true);
    }
} 

Answer 2

关键事件仅调度到具有焦点的组件。默认情况下，JPanel 不可聚焦，因此它永远不会接收关键事件。

更好的方法是使用 KeyBinding，即使事件没有焦点，它也可以响应事件。请参阅使用键盘的动作以获取更多信息和工作示例。